The e-ILV provides free access to all the terms and definitions contained in the international standard CIE S 017:2020 ILV: International Lighting Vocabulary, 2nd edition.

To search for another term please use  "Back to the list" to return to the main page or the e-ILV.

For the complete set of terms and definitions CIE S 017:2020 can be purchased from the CIE Webshop. Members of a CIE National Committee or Associate National Committee have access to a 66,7 % discount on the purchase price of the standard.

For advice on CIE Publications contact Note the CIE Helpdesk cannot assist with technical enquiries.


Napierian spectral absorbance, <of a homogeneous non-diffusing layer>

Napierian spectral internal transmittance density

An(λ); B(λ)

natural (Napierian) logarithm of the reciprocal of the spectral internal transmittance, τ(λ)
An(λ) = B(λ) = − ln τ(λ)

Note 1 to entry: The Napierian spectral absorbance has unit one.

Note 2 to entry: This entry was numbered 845-04-84 in IEC 60050-845:1987.

Note 3 to entry: This entry was numbered 17-798 and 17-800 in CIE S 017:2011.

Publication date: 2020-12
Copyright © CIE 2020. All Rights Reserverd.